Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $229.61   5.475%   $242.1811   $242.18   $242.20   $242.20  
  Purchase #2 $170.49   5.453%   $179.7868   $179.79   $179.80   $179.80  
  Purchase #3 $52.27   11.251%   $58.1509   $58.15   $58.15   $58.20  
  Purchase #4 $240.33   5.528%   $253.6154   $253.62   $253.60   $253.60  
  Purchase #5 $218.57   10.668%   $241.887   $241.89   $241.90   $241.90  
  Purchase #6 $55.61   9.438%   $60.8585   $60.86   $60.85   $60.90  
  Purchase #7 $206.43   11.578%   $230.3305   $230.33   $230.35   $230.30  
  7 purchase totals = $1,173.31       $1,266.8102   $1,266.82   $1,266.85   $1,266.90